The present invention relates to a method and apparatus for the deposition, etch, and/or thermal processing of thin films in physical vapor deposition ( PUD) systems.
Processing of increasingly pure and uniform thin films of a wide variety of materials onto an equally wide variety of types and sizes of substrate materials is a key processing requirement in the manufacture of many high technology products including integrated circuits, magnetic and optical memory media, active and passive solar energy devices, and optical coatings. There are several types of processes that may be carried out in PUD systems including thermal evaporation, ion-beam etching and magnetron sputtering, and molecular-beam epitaxy to mention just a few.
A common problem with each of these processes is how to uniformly process high-purity homogeneous films over any given substrate area, while maintaining acceptable commercial throughputs and source efficiencies. This problem is illustrated in FIG. 1 for the particular case of a ring magnetron sputtering source, although the following discussion is equally applicable to all sources commonly utililized in PUD systems. As shown in FIG. 1, the distribution of sputtered material at the substrate plane is highly nonuniform. The amplitude (deposition rate) and shape (profile) of this distribution depend not only on the type, design, and operating conditions (e.g., deposition chamber pressure) of the source, but also on the particular source material (target), the state of erosion (usage) of the source material, and the source-to-substrate spacing. (Note that the properties of the substrate may also influence the source distribution. For most sources on PUD systems this influence is typically small and/or predictable. This is to be contrasted with other thin film processing techniques such as chemical vapor deposition (CUD), where the effect of the substrate on the deposition may be a dominate factor.)
The PUD equipment industry had developed the following techniques for achieving more uniform processing of thin films:
a. Use processing sources much larger than the substrates.
b. Use tuning electric and magnetic fields, shadow masks, etc. to shape the source distribution.
c. Use substrate motion to average the source distribution.
d. Various combinations of the above.
The problem with the first brute-force technique is its obvious inefficiency. Not only is it wasteful and expensive, especially for precious metal depositions, the use of very large sources sets off a chain reaction of increased size and cost and reduced versatility in the PUD equipment design and performance. In particular, research and development (R&D) in a production PVD system (or vice-versa) is a difficult, expensive, and unrewarding undertaking. Using separate systems for R&D and production is one approach, but this requires that processing techniques developed on an R&D system be efficiently and accurately transferred to a production system. This time required in getting the product out of the laboratory and into production is one of the major problem areas in the industry.
The source size can be reduced substantially by using various techniques to shape the source distribution to give more uniform thickness deposition. However, this approach also has its problems. First, because each point on a fixed substrate has a different spatial relationship to an extended source, the homogeneity of the film can vary substantially over the substrate even when its thickness is uniform, especially for reactively deposited films. Second, each source material has different shaping requirements which makes this approach tedious and time consuming. Finally, as the source material erodes away its deposition profile changes, requiring that its source distribution be re-shaped or that it be replaced with a new target, often after only a few percent target utilization.
Various types of substrate motion, when combined with the above techniques for controlling the source distribution, are quite effective in minimizing many of the problems cited above. Mobile planetary substrate fixturing used in the industry is illustrative of this approach. These are typically constant speed mechanisms with one or more degrees of freedom designed to average the source distribution over large substrate areas in a manner that produces more uniform processing. The advantages of reduced source size and improved uniformity that result from substrate motion during the processing are quite significant, assuming that the processing environment is sufficiently clean to assure very pure processing even though the substrate repeatedly moves in and out of the processing area as a consequence of this motion. However, as currently implemented by the PVD equipment industry, these planetaries do no more than average differences in source distributions, such as those due to different source materials and states of erosion. Furthermore, constant speed planetaries are highly inefficient when used for R&D because they are designed for achieving uniform processing over the entire planetary surface, not just selected smaller portions that would be more appropriate for R&D applications.
As a result, no better than 90-95% process uniformity is the current advertised state-of-the-art performance specification for PVD equipment using various combinations of these shaping and averaging techniques, while also maintaining useful product throughputs and source efficiencies.